Production of food-grade multiple emulsions with high encapsulation yield using oscillating membrane emulsification

Food-grade water-in-oil-in-water (W/O/W) multiple emulsions with a volume median diameter of outer droplets of 50–210 μm were produced by injecting a water-in-oil (W/O) emulsion at the flux of 30 L m−2 h−1 through a 10-μm pore electroplated nickel membrane oscillating at 10–90 Hz frequency and 0.1–5 mm amplitude in 2 wt% aqueous Tween® 20 (polyoxyethylene sorbitan monolaurate) solution. The oil phase in the primary W/O emulsion was 5 wt% PGPR (polyglycerol polyricinoleate) dissolved in sunflower oil and the content of water phase in the W/O emulsion was 30 vol%. The size of outer droplets was precisely controlled by the amplitude and frequency of membrane oscillation. Only 3–5% of the inner droplets with a mean diameter of 0.54 μm were released into the outer aqueous phase during membrane emulsification. A sustained release of 200 ppm copper (II) loaded in the inner aqueous phase was investigated over 7 days. 95% of Cu(II) initially present in the inner water phase was released in the first 2 days from 56-μm diameter multiple emulsion droplets and less than 15% of Cu(II) was released over the same interval from 122 μm droplets. The release rate of Cu(II) decreased with increasing the size of outer droplets and followed non-zero-order kinetics with a release exponent of 0.3–0.5. The prepared multiple emulsions can be used for controlled release of hydrophilic actives in the pharmaceutical, food, and cosmetic industry.